Reproductive Strategies

1. Reproductive Strategies BIOL 435

2. Concepts of Evolution & Fitness • Evolution • Natural selection • Sexual selection • Fitness • Kin selection • Group selection • Reproductive strategy • Behavior • Evolutionarily Stable Strategy • Optimality Theory • Comparative Method • Panglossian paradigms

3. Evolution • Definitions: • Change in allele frequencies over time • Change in properties of populations that transcend lifetime of single individual • Process that results in heritable changes in a population spread over many generations • Mechanisms of evolution • Mutation • Migration • Genetic Drift • Natural Selection • Sexual Selection, Co-evolution, Kin/Group Selection

4. Horizontal gene transfer • Transfer of genetic material between two different species • Mitochondria • Chloroplasts • Jumping genes, transposons • Viruses • Can result in • Expression of foreign DNA in organism • New species Rumpho et al 2008 PNAS

5. Tenets of Natural Selection • Variation exists • That variation is heritable • More offspring are produced than can survive • Survival is not random (differential mortality) Variation: Individuals in the population must differ with respect to the trait in question. Heritability: The variation found in the population must (at least partially) transmitted from parent to offspring. Differential Mortality: Finally, individuals must have a probability of survival that is a function of the value of the trait in question.

6. Units of Evolution • Unit of selection • Individual • Unit of evolution - adaptation • Gene or Population • Unit of evolution - speciation • Population Species

7. Sexual Selection • Subset of Natural Selection • Natural Selection • Selection for traits that increase an individual’s ability to survive or reproduce • Sexual Selection • Selection for traits that increase an individual’s ability to reproduce • Textbook definition - Selection for traits that increase an individual’s ability to acquire mates • To study sexual selection, we must examine the behaviors or traits that increase an individuals ability to acquire mates, fertilize eggs, produce zygotes, and raise offspring

8. Reproductive Strategy • Definitions • A life history trait or collection of traits that results in survival and reproductive success • Genetically determined behavior that has evolved because it maximizes fitness under frequency dependent intraspecific competition (Gross 1987) • Reproductive strategies include • Type of reproduction (sexual versus asexual), Gender systems , 1° and 2° sexual characteristics • Number and pattern of matings • Location and method of fertilization and nest site • Type and amount of parental care

9. Mammalian Reproductive Strategies • Spotted Hyenas, Crocuta crocuta • Live in communal dens • Females clitoris resembles penis • Labia fused to form “scrotum” • Pseudopenis used to urinate, mate, give birth • Females larger, more aggressive • Alpha female • Males leave natal group at 2 or 3 • Takes 2 years to fight for acceptance in new group and mate • Females have 100% mate choice Female

10. Avian Reproductive Strategies • Bowerbirds • Polygynous (1 male to 25 females) • Complex male display behavior • Bower • Decoration display • Colors vary with habitat • Elaborate vocal/dancing courtship • Bower may allow female choice, protect female from forced copulation • Male-male courtship displays in juvenile males in order to learn http://www.youtube.com/watch?v=tJ32_ijdmLo&feature=related http://www.youtube.com/watch?v=Ii2D9Bd5OoE&feature=related

11. Invertebrate Reproductive Strategies • Banana Slugs • Hermaphrodites (male and female functions) • Penises inserted reciprocally or unilaterally into other’s female tract • Occasionally bite off partner’s penis (apophally) • Penis consumed by recipient

12. Fish Reproductive Strategies • Anglerfish (Borophryne) • Females 10x size of males (20-40 mm) • Males parasitic on females • Find and attach by mouth, skin fuses, rely of female for nutrition • Internal organs degenerate except for testes ♂ ♂

13. Primate Reproductive Strategies • Chimpanzees (Pan troglodytes) • Male dominance hierarchy • Females disperse from natal groups during period of adolescent infertility • No evidence of birth season, estrous correlated to food • Females mate promiscuously & opportunistically with many males • Restrictive mating • Consortship mating • Extra-group mating • Males practice infanticide

14. Plant Reproductive Strategies • Monoecious and dioecious • Self-pollinated or out-crossing • Angiosperms • Wind Pollinated • Pollen shape/specificity • Animal Pollinated • Use of heterospecifics to mate • Orchidaceae

15. Orchid deception • Pseudocopulation • Mate mimics • Ophyrus species have flowers that look like female bees, secrete a terpene compound that is a bee pheromone • Prey mimics • Epipactis species have structures that look like aphids, visited by flies whose larvae eat aphids • Aggressive mimics • Oncidium species have flowers at the ends of stalks that sway in breeze, Centris bees mistake flowers for male competitors and attack them

16. Prokaryotic Reproductive Strategies • Slime molds • Diverged from animal-fungi lineage before animals diverged from plants • Haploid spore germinates to form flagellate cells or amoeboid cells • Cells may act as isogametes, form zygote • Zygote grows into plasmodium, nucleus divides many times, but cells don’t - Mature plasmodium has 1,000s nuclei in 1 giant cell • Zygote undergoes meiosis, forms amoebas, amoebas aggregate and form fruiting bodies with some amoebas “sacrificing” themselves to form stalk • 3 genes control types of gametes (sexes) with 2 of these genes having 13 variants Dictyostelid slime mold Judson pp. 187-193

17. Elements of Reproductive Strategies • Reproduction • Sexual/Asexual • Gender system • Gonochoristic • Hemaphroditic • Sequential/Simultaneous • Parthenogenetic • Gynogenetic/Hybridogenetic • Number of broods/matings • Semelparous • Iteroparous • Single season/multiple season • Mating system • Inbreeding/outbreeding • Promiscuous • Polygamous • Monogamy/Polygyny/Polyandry • Place of fertilization • External • Internal • Buccal • 1° sexual characteristics • Genetics of gender • Types of genitalia • 2° sexual characteristics • Monomorphic/Dimorphic/Polymorphic • Permanently/Seasonally dimorphic • Mating site preparation • None, Prepared, Prepared & defended • Parental Care • None • Female or male • Biparental • Juvenile/kin helpers

18. Evolution of Behavior • Is behavior genetic? • Resistance to idea that behavior is genetic because “genes for” behavior suggests genes control all that we do • Gene for white eyes in drosophila • Single gene does NOT control production of entire eye • Single gene IS responsible for difference between white eyed and red eyed individuals

19. Evolution of Behavior • Examples of “genes for” behavior in reproductive strategies • Genes in male cricket determine nerve impulses to wings • Controls pattern of singing to attract mates • Gene inversion creates tan & white morphs of white-throated sparrows • White males spend less time guarding mates, are more aggressive, provide less parental care, and are polygynous • 2 genetic strains of parasitic wasps • Differ in ovary morphology with one strain producing fewer eggs Tree cricket singing

21. Evolutionarily Stable Strategy • Definition • A set of behaviors or traits (phenotype) that when adopted (evolved) by most members of a population cannot be invaded by the spread of any rare alternative behavior or trait (has higher reproductive success than other phenotype(s)) • Strategy– specification of what the animal does • Examples • “Produce 50% sons and 50% daughters” • “Always escalate a fight with a smaller male until male retreats” • “Mate with any available female” • Evolutionarily Stable • Once adopted by all members of a population, the strategy has a higher reproductive success than any alternative strategy that might arise Maynard Smith & Price (1973) Nature

22. Frequency dependent selection • Natural selection • Look for higher reproductive success of one trait or strategy over another • Individuals that always escalate to fighting have more offspring that those that retreat • However, degree of success of one trait often not a fixed value but varies with the presence of other traits • If all individuals fight, most risk severe injury and suffer reduced fitness • “Frequency dependent selection” • Degree to which a strategies is successful depends on how many others in the population are employing it

23. ESSs depend on Frequency Dependent Selection • Hawk • “Always escalate a fight until injured or opponent retreats” • Dove • “Display but retreat at once if opponent escalates” • Hawk strategy successful if most of population are Doves • But, superiority when rare does not allow it to spread • As Hawk strategy becomes more common, Hawks get injured in confrontations with other Hawks • Doves never get injured because they always retreat • Fitness of either strategy depends on reproductive costs and benefits

25. Evolutionarily Stable Strategy • ESS requires that variation in behavior exists in population • Can be instances in which a mixture of 2 or more strategies are ESSs • Example: Uta stansburiana, side-blotch lizards • Orange males – aggressive, territorial, polygynous, also usurp territories of other males • Yellow males – non-territorial, sneak mates by mimicking females • Blue males – guard mates, chase off yellow males, but run from orange males, establish territories near other blue males and cooperate in mate defense

26. “Proving” selection • Intractable to demonstrate that current traits are outcome of selection • Can develop testable predictions about value • 1) assume individuals are acting to maximize fitness (genetic contribution to next generation) • 2) suggest how trait might contribute • 3) predict under what conditions benefits exceed costs • 4) perform experiments that measure costs and benefits by counting number of offspring produced under different conditions

27. Optimality Theory • Selection should result in optimal traits • Optimal trait: characteristic whose benefit to cost ratio is greater than that of alternative phenotypes • Traits will converge on point where benefit to cost ratio is greatest • Difficulties in testing for optimality • Math may be complex (i.e. may not be able to assess all costs and benefits) • Can’t always test (or know) all alternative strategies • Requires making simple assumptions and excluding some parameters Benefit or Cost B – C = max Trait value

28. Comparative method • Is there a correlation (across species) between an environmental factor and possession of a trait? • Example: When females are highly dispersed and hard to find, males should guard single female • Convergent evolution on same reproductive strategy under same conditions • Problems with comparative method • Non-experimental • Could be the result of other factors that correlate to those investigated Africa (left) – Hippo, chevrotain, antelope, duiker, armadillo Neotropics (right) – Capybara, paca, agouti, deer, pangolin

29. Individual vs. Kin Selection • Kin Selection • Increase in frequency of traits because they are passed on by the relatives (kin) of individuals who express the traits • “Inclusive fitness” • “Extended phenotype” • Evolves when BR – C > 0 or R > C/B • B = benefit: increase in offspring number of relative • R = degree of relatedness between altruist and relative • C = cost: decrease in offspring number of altruist when helping relative • Parental care may be viewed as Kin Selection

30. Individual versus Group Selection • Group selection • Traits of individuals evolve because they contribute to survival of group or species as a whole • Example: By gathering in groups (leks) males make it easier for females to locate mates • Alternative: A female that observes multiple males simultaneously will be able to choose best mate more rapidly • Conditions for group selection to occur same as for kin selection (benefit and inclusive fitness outweigh cost), but individual act in own interest

31. Panglossian Paradigm • “Everything is made for the best purpose” • Problems with seeking adaptive explanation for all traits • Selection acts on entire individual • Pleiotropic effects • Genes for different traits linked on same chromosome, indirect selection • Phylogenetic constraints • Selection acts on traits organisms have already evolved, restricted by individuals current phenotype • Evolutionary lag time, traits may be maladaptive under new conditions • Genetic drift • Traits may become fixed through drift or bottlenecks • Allometry • Traits constrained by geometry • Exercise restraint in attributing adaptive value to any given trait, and especially to all traits Gould and Lewontin (1979) Thornhill & Alcock pp. 9-13

32. Examples of “Just So Stories” • “Size matters” Neufeld and Palmer (2008) • Variability in penis size in clams result of selection by females • Penis shape is phenotypically variable & correlated with hydrodynamic conditions • “Baby got back” • Human female butts protrude as advertisement to males of reproductive potential • Gluteus muscle size and fat storage are allometric result of evolution of bipedalism and of gravitational constraints? • Rape is adaptive • Requires demonstration that men who rape have greater reproductive fitness than men who do not